Keyswitch-integrated pointing assembly

ABSTRACT

A keyswitch-integrated pointing assembly in which a plurality of substantially planar force sensing elements are disposed on a planar surface adjacent a keyswitch on a keyboard. The keyswitch includes a plunger which extends downwardly from a key cap for actuating a switch at the lower end of vertical key cap travel. The key cap engages an indexing surface when fully depressed which transmits force applied to the key cap to the force sensing elements. The force sensing elements are sandwiched between a pair of opposing plates thereby biasing the elements into a substantially linear operating region when no force is applied to the key cap.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to apparatus for controllingcursor movement on a cathode ray tube (CRT) and more particularly tosuch apparatus which is integrated with a keyswitch on a keyboard.

2. Description of the Related Art

Prior art pointing devices for controlling a cursor on a CRT are known.What others have failed to appreciate is the ergonomic implications ofmechanical and electrical null regions which must be traversed at theoutset of a pointing operation. Using prior art devices, even those thatare force-sensitive, a user gets no response to lateral displacementinitially, until an electrode makes initial contact, for example, withan elastomeric resistive layer. The initial contact causes a stepresponse, as resistance drops from infinity to a measurable value--ajump the user may not have anticipated or desired. Then, as force isincreased, resistance falls rapidly, over some range, and finally fallsmore slowly with the application of additional force. All of this isdisconcerting to a user for most applications. What is needed is toprovide for pointing which is smoothly and consistently responsive touser input from the outset of the pointing operation.

Another disadvantage associated with prior art devices is that they arenot sensitive to z-axis force. Forces applied laterally, i.e., in thex-y axis plane move the CRT cursor correspondingly. It would bedesirable for a vertical force, e.g., down the shaft of a joystick-typecontroller, to produce a proportional signal. Such a signal could beused for example to control line width while drawing as a function ofz-axis force on the pointing device.

Pointing devices which are integrated into keyswitches on keyboards arealso known in the prior art. In addition to suffering from theabove-described disadvantages associated with prior art pointingdevices, such integrated devices take up substantially more space than aconventional key switch.

One prior art cursor control is shown in U.S. Pat. No. 4,313,113(Thornburg). It employs four orthogonal variable resistance pressuretransducers, each transducer comprising a coordinate electrode spacedfrom a cooperating electrode, at least one of the electrodes being anelastomeric sheet material formed of a carbon loaded polyolefin. Thepath resistance through the transducer goes down as applied pressuregoes up. Thornburg recognizes the advantage of using force to controlcursor speed. It makes no suggestion to integrate the device into aregular keyswitch. The electrodes are spaced from the elastomeric layer,at rest, so that there is a mechanical and electrical null region beforethe system responds to a force input, followed by a step response whenthe electrode layers make initial contact.

U.S. Pat No. 4,439,648 (Reiner et al.) is directed to a basicstand-alone joystick. The handle rests on a rigid pivot so that verticalforce is ignored. The handle is coupled to an actuator portion spacedfrom all four switches, so there is a neutral or null region ofdisplacement before any switch is closed. The switches are conventional,yielding only a binary signal, without regard to force.

U.S. Pat. No. 4,408,103 (Smith, III) discloses a miniaturized joystickadapted for mounting in a wristwatch. The joystick handle rests in ahollowed-out bearing surface so that none of the switches is actuated bya downward force on the handle. The switch actuating means is maintainedspaced from all the switches by a resilient rubber sheet layer, so thereis a neutral or null region of displacement before any of the switchesis closed. The switches are miniaturized by forming them as interleavedelectrodes on a PCB. When the handle is pivoted, an actuator pushes aconductive region of the resilient layer into contact with acorresponding switch. The switches each yield a binary output, solateral force beyond an initial detent is ignored.

U.S. Pat. No. 4,246,452 (Chandler) shows another joystick type device,here having 16 possible output signals. The mechanism again employs ahandle having a depending member that rests in a hollowed out bearingsurface. Once again, the switches each provide a binary signal,independent of lateral force beyond a threshold force; vertical force isignored; and, the actuator is spaced from the switches to provide a nullregion.

U.S. Pat. No. 4,680,577 (Straayer et al.) suggests a multipurpose cursorcontrol keyswitch that serves both as a regular typing key, preferablyin the "home row" (asdf-jkl;) of a keyboard, as well as aforce-sensitive pointing input device. The use of strain gauges as showntherein for force sensing, however, is not commercially practical.Additionally, the recent rise in popularity of portable, lap-top and now"notebook" computers makes low profile methods essential.

SUMMARY OF THE INVENTION

The present invention comprises a pointing device having a referenceplate and a generally planar force sensing means mounted on thereference plate. An actuator applies force to said force sensing means.The actuator and force sensing means are interconnected so that lateraland vertical forces applied to said actuator are transmitted to saidforce sensing means. In another aspect of the present invention, thepointing device is integrated with a keyswitch on a keyboard.

It is a general object of the present invention to provide akeyswitch-integrated pointing assembly which overcomes theabove-enumerated disadvantages associated with prior art devices.

It is another object of the present invention to provide such anassembly which smoothly distributes forces between sensing elements.

It is still another object of the present invention to provide such anassembly which moves the operating point of the force sensing elementsinto a continuous, smoother, region of operation.

It is yet another object of the present invention to provide such anassembly having generally opposed sensors which are loaded and unloadedin a complementary fashion.

It is another object of the present invention to provide such anassembly which is relatively low profile in structure and which ismanufactured with relatively low dimensional tolerance sensitivity.

The foregoing and other objects, features and advantages of theinvention will become more readily apparent from the following detaileddescription of preferred embodiments which proceeds with reference tothe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a first embodiment of aelastomeric dome keyswitch and integrated pointing assembly according tothe present invention.

FIG. 2 is a cross-sectional view taken along line 2--2 in FIG. 1.

FIG. 3 is an exploded perspective view of an alternative embodiment of aelastomeric dome keyswitch and integrated pointing assembly according tothe present invention.

FIG. 4 is a cross-sectional view taken along line 4--4 in FIG. 3.

FIG. 5 is an exploded perspective view of a first embodiment of adiscrete keyswitch and integrated pointing assembly according to thepresent invention.

FIG. 6 is a cross-sectional view taken along line 6--6 in FIG. 5.

FIG. 7 is an exploded perspective view of an alternative embodiment of adiscrete keyswitch and integrated pointing assembly according to thepresent invention.

FIG. 8 is a cross-sectional view taken along line 8--8 in FIG. 7.

FIG. 9 is an exploded perspective view of an elastomeric dome keyswitchand integrated pointing assembly including a pre-load spring assemblyaccording to the present invention.

FIG. 10 is a cross-sectional view taken along line 10--10 in FIG. 9.

FIG. 11 is a cross-sectional view similar to FIGS. 2 and 4 showing thepreload means located beside the switch mechanism instead of above orbelow it.

FIG. 12 is a partially broken-away top view of a keyboard, with the Jkeycap removed, showing a mechanism similar to that of FIGS. 1 and 2having three force sensing areas instead of four.

FIG. 13 is a plot of force versus resistance for an FSR™ force sensingresistor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is an exploded perspective view of a first embodiment of anelastomeric keyswitch and integrated pointing assembly according to thepresent invention. Beginning roughly in the middle of the diagram, aconventional elastomeric type keyboard includes a base plate 30, suchbeing also referred to herein as a reference plate, which is generallyplanar. The base plate may be of any suitable rigid material, such as aplastic or metal, or it may be a printed circuit board. For manyapplications, the base plate 30 is a printed circuit board and itincludes a plurality of switch contacts 32, like contacts 32, formed onthe printed circuit board so that switch closure is effected by downwardpressure on the switch contacts. This type of keyswitch is commonly usedin a computer keyboard, in which an array of such switch contacts areformed on the base plate in a predetermined pattern corresponding to thepattern of the typing keys.

A conventional elastomeric keyboard also includes a rubber dome sheet20. The rubber dome sheet includes an array of dome springs, like domespring 21, which provide a spring action that biases the keyswitch tothe standby open position. The rubber dome sheet 20 is registered overthe base plate 30 so that each dome spring 21 is aligned over arespective one of the switch contacts 32. In some designs, the switchcontacts 32 on the base plate comprise an interleaved set of conductivefingers. In that case, the underside of the dome spring 21 includes aconductive pad which, when pressed against the interleaved fingers,completes an electrical path between the fingers thereby closing theswitch.

Alternatively, in a membrane type keyswitch, the switch may comprise avertically spaced pair of electrodes in which case the underside of domespring 21 need not be conductive, but merely arranged to impart verticalforce to close the switch. A plunger guide 14 rests on top of the rubberdome sheet 20. The rubber dome sheet is silicone with a 30-50 Shore "A"durometer. The plunger guide 14 includes a central aperture 16, furtherdiscussed below. The plunger guide 14 is positioned with the aperture 16aligned over the dome spring 21 and switch contacts 32. In the presentembodiment of the invention, plunger guide 14 is polycarbonate. Theplunger guide 14 also includes a tower portion 15 extending about theperiphery of aperture 16. The tower portion 15 includes an upper surface18, hereafter referred to as the actuator indexing surface.

A conventional key cap 10 is coupled to a depending plunger 12. In somecases, the key cap and plunger are molded of a single part, and in othercases they may be formed of separate parts and engage one another. Theaperture 16 is sized to fittingly engage the plunger 12 while allowingvertical sliding motion of the plunger responsive to a vertical forceapplied to the key cap by an operator.

A force-sensing resistor array 22 is positioned between the base plate30 and rubber dome sheet 20. The force-sensing resistor array 22includes a central aperture 28, sized to clear the plunger 12 and switchcontacts 32. The array 22 is positioned so that the aperture 28 isregistered with the plunger guide aperture 16, dome spring 21 and switchcontacts 32. In a typing mode of using the apparatus, a generallydownward pressure is applied to the key cap 10 by an operator. The keycap and plunger 12 move downward together, with the plunger slidingthrough the plunger guide aperture 16. The bottom end of the plungercontacts dome spring 21 and compresses the dome sheet so that theunderside of the dome spring 21 contacts the switch contacts 32 on thebase plate. Accordingly, the force-sensing resistor array 22 does notinterfere with, or in any way affect, the usual operation of thekeyswitch.

Vertical travel of the key cap and plunger is limited to a position inwhich the key cap indexing surface 11 contacts the actuator indexingsurface 18. The key cap indexing surface 11 and actuator indexingsurface 18 have complementary configurations for mating with oneanother. They may simply be flat, for example, or they may be tapered,stepped, or the like, to aid in guiding the plunger and to contribute toa solid coupling between the key cap and plunger, on the one hand, andthe plunger guide/actuator 14 on the other hand, when the key cap is ina depressed state.

A pre-load pad 34 is positioned in parallel contact with the undersideof base plate 30. A rigid back-up plate 36 is positioned in parallelcontact with the underside of pre-load pad 34. The back-up plate 36,pre-load pad 34, base plate 30, force-sensing resistor array 22, andrubber dome sheet 20, all have a plurality of mounting holes, preferablyarranged symmetrically about the neutral axis. The neutral axis, as usedherein, refers to a vertical axis through the center of apertures 16,28, dome spring 21, etc. in FIGS. 1 and 2 and to a corresponding centralaxis in each of the other embodiments. The plunger guide/actuator 14includes corresponding mounting holes, at least extending into theunderside of the plunger guides/actuator, for receiving fastening meanssuch as fasteners or screws 38. The screws 38 extend through the back-upplate, pre-load pad, base plate, force-sensing resistor array, rubberdome and rubber dome sheet and are threadably secured in the plungerguide/actuator for maintaining the foregoing elements in the positionsdescribed. As can be seen in FIG. 2, the bores in plates 30, 36; pad 34;array 22; and sheet 20 through which screws 38 extend are sized to leavean annular space as shown between the shaft of each screw 38 and thebores through which it is received. With the end of each screwthreadably secured in guide/actuator 14, the guide/actuator may thus berocked or tilted about the neutral axis in a manner and for a purposewhich is described in more detail hereinafter. The fasteners 38 could beintegrally formed with the back-up plate 36 or guide/actuator 14.

Operation of the elastomer key switch and integrated pointing assemblyof FIG. 1 is best understood with reference to a cross-sectional view ofthe same assembly shown in FIG. 2. FIG. 2 shows the assembly of FIG. 1in the standby state, i.e., when no external force is applied to the keycap 10. This cross-sectional view illustrates a flat configuration ofthe indexing surfaces 11, 18.

The actuator 14 includes four actuator surfaces 17, protruding from theunderside of actuator 14 and positioned so that each of the actuatorsurfaces 17 contacts a respective one of the force-sensing resistorelements 24 in the array 22. Preferably each of actuator surfaces 17 aresubstantially in the shape of a spherical segment. The rubber dome sheet20 extends between the actuator surfaces 17 and the correspondingforce-sensing elements 24. This has been found to be advantageous inthat the rubber dome sheet smoothly disperses or distributes forcesapplied through the actuator surfaces 17 to the force-sensing element24. The base plate 30 provides a relatively rigid support to theunderside of the force-sensing array 22 so that forces applied throughthe actuator surfaces 17 are efficiently coupled to the force-sensingarray. The actuator 14 includes a hollowed out portion on the underside,defined by a surface 19, so that the actuator 14 does not contact thedome spring 21. The actuator therefore does not interfere with the usualtyping operation.

The height of the tower portion 15 of the actuator is sized to cooperatewith the key cap and plunger to limit vertical displacement of thekeycap and plunger to a position sufficient to actuate switch contacts32, but no further. Once the indexing surfaces 11, 18 are contacting oneanother, substantially all forces applied to the key cap by an operator,vertical as well as lateral, are transmitted through the plunger andactuator to the force sensor array.

As noted with regard to FIG. 1, the actuator 14 is coupled to theback-up plate 36 by suitable rigid fasteners 38. The pre-load pad 34,extending between the back-up plate 36 and the base plate 30 is formedof a compressible material such as a closed cell foam. In the presentembodiment of the invention, pre-load pad 34 comprises a polyurethanefoam with a low compression set. During manufacture, the fastening meansare applied so as to partially compress the pre-load pad 34. Thisarrangement holds the entire assembly together without play and, moreparticularly, applies a pre-load force to each of the force-sensingelements 24.

Applying a pre-load force to the force-sensing resistor elements 24 isimportant for the following reasons. First, force-sensing resistorelements, for example a device sold under the trade name FSR™ byInterlink, Inc. of California, provide essentially infinite resistancewhen no force is applied to the element. When even small initial forceis applied, on the order of a hundred grams, the FSR™ elements instantlydrop to an initial resistance on the order of a few hundred thousandohms. This drastic change, or step response, is disconcerting to anoperator and undesirable for most applications. The application of apre-load force to the FSR™ device eliminates this initial step responseproblem.

Second, even after a small initial force is applied, FSR™ elementsexhibit resistance to force characteristics that initially changes veryquickly, for example, exponentially, and, as force is further increased,moves into a more linear region of operation. By arranging a pre-loadforce to bias the FSR™ elements into this more linear region ofoperation, the devices will exhibit a more linear response to externalforces applied by the operator.

It may be observed that the key cap 10 is entirely supported by thestructures shown in FIG. 2. In a conventional keyboard, the key cap andplunger are supported by a plunger guide having a central aperturesimilar to aperture 16 in actuator 14, but the guide generally is partof a continuous molded plate that includes a guide for each of the keyswitches in a keyboard array. Here, the plunger guide is formed in theactuator 14, which must be isolated from the rest of the keyswitch arrayto provide for imparting lateral forces for pointing operations. Thestructure shown in FIG. 2, therefore, is freestanding, except that it ismounted on the base plate or printed circuit board 30.

In normal keyswitch operation, as noted, the pointing device apparatusdoes not affect the switch operation. The tactile response or "feel" ofthe keyswitch is the same as an unmodified keyswitch, in that it isdetermined by the usual dome spring 21 on the rubber dome sheet 20. In apointing operation, the indexing surfaces 11, 18 contact each other sothat all forces imparted to the key cap 10 by an operator aretransmitted to the actuator 14 and, through the actuator surfaces 17, tothe force-sensing array 22. As noted above the force-sensing elementsare pre-loaded to a predetermined operating point, so that a lateralforce applied to the key cap 10, for example, along the X or Y axis,results in a differential signal in that the force applied to one of theforce-sensing elements 24 is increased while the force applied to theforce-sensing element opposite the first force-sensing element isdecreased. A force applied in any direction off the X or Y axis resultsin resistance to change in all four sensing elements.

Noteworthy is the absence of any pivot type supporting means as in aconventional joystick. According to the present invention, the keycapand plunger are supported, in the depressed state, by the actuator 14.Accordingly, downward or Z direction forces are coupled through theactuator surfaces 17 to the sensing array 22. The present apparatusthereby measures the overall or net force applied by an operator. Thenet force can easily be computed by summing the forces on all thesensors. The net applied force information is useful in manyapplications, for example, to control cursor speed, or to provide Z axiscontrol. Increasing the apparent cursor speed in response to a greateroperator applied force provides a natural and ergonomically efficientresponse.

The pre-load pad 34 also affords the advantage of neutralizingmanufacturing variations in the various components described, as well asobviating a pivot's high tolerance requirements. In use, the compressedpre-load pad 34 takes up variations in thickness of the elements inbetween the backup plate 36 and the actuator 14 to avoid any play orwobble in the system. As long as the force-sensing elements are biasedto some reasonable operating point, a processing unit coupled to theforce-sensing array can be arranged to calibrate itself to define zeroforce as whatever resistances are provided by the force-sensing elementsin the absence of externally applied forces.

Elimination of the pivot type supporting means also allows the presentinvention to avoid interference with the operation of the existingkeyswitch means.

FIG. 3 is an exploded perspective view of an alternative embodiment ofan elastomer keyswitch and integrated pointing assembly according to thepresent invention. Referring to FIG. 3, the assembly again includes abase plate 30, a force-sensing array 22, rubber dome sheet 20, keycap10, and plunger 12, all of which are similar to those described withregard to FIGS. 1 and 2. Here, the existing keyboard or other device isassumed to include a fixed top plate 40. The top plate 40 may be part ofa larger plate that forms part of a keyboard array or, for example, maybe part of a rigid enclosure. Plate 40 includes a central aperture 42which is sized to provide clearance around the guide tower 47 to allowlateral displacement f the tower. For some applications, in which theexisting aperture 42 is sized to fittingly engage the plunger forguiding the plunger, it may be suitably enlarged for implementing theintegrated pointing assembly. A combined plunger guide and actuator 46(hereafter "actuator") is positioned, as before, to rest on the existingrubber dome sheet 20, albeit without contacting the dome spring portion21. Actuator 46 includes a central aperture 49 sized to fittingly engagethe plunger 12 while allowing sliding motion of the plunger responsiveto the vertical depression of the keycap. The actuator 46 also includesa tower portion 47 extending about a periphery of the aperture 49 andincluding an actuator indexing surface 48 for contacting a complementarykeycap indexing surface 11 (shown in FIG. 4) on the underside of thekeycap.

A preload means 44, in this case a foam pre-load pad, includes a centralaperture 45 sized to clear the tower 47 so that the pre-load pad 44rests on the peripheral flange portion of actuator 46.

FIG. 4 is a cross-sectional view of the assembly of FIG. 3 in a standbyposition, i.e., in the absence of externally applied forces. Actuator 46includes a hollowed out portion on the underside so that it does notcontact the dome spring 21. The actuator 46 includes actuator surfaces50 protruding from the underside of the actuator, each of which ispositioned over a respective one of the force sensor elements 24.

As before, the rubber dome sheet 20 extends between the actuatorsurfaces 50 and the corresponding force sensor elements for distributingapplied forces. As noted, the aperture 42 in top plate 40 provides aspace between the actuator 46 and top plate 40 extending around theentire periphery of the aperture 42, so that, even when a lateral forceis applied to deflect the keycap and plunger off the neutral axis, theactuator does not contact the top plate 40. The pre-load pad 44 ispositioned between the peripheral flange portion of the actuator 46 andthe underside of support plate 40.

In the typical keyboard application, the support plate 40 is fixed tothe base plate 30, independently of the structures here described. Forexample, a typical keyboard may have screws or other fastenersinterconnecting top and bottom plates at several locations. Such anarrangement may be adequate to hold the structures of FIGS. 3 and 4 intheir intended positions. However, it may be preferable, depending uponthe particular application, to provide fastening means forinterconnecting the support plate 40 to the base plate 30 in one or morelocations adjacent the integrated assembly of FIGS. 3 and 4 to ensureappropriate pre-loading of the force-sensing elements as describedabove. This is illustrated in FIG. 4 as fastener 39. Although thepre-loading pad is arranged differently in the embodiment of FIGS. 3 and4, it functions essentially in the same manner and provides the sameadvantages as described above with respect to FIGS. 1 and 2.

FIG. 5 is an exploded perspective view of a first embodiment of adiscrete keyswitch and integrated pointing assembly according to thepresent invention. The term "discrete keyswitch" is used here to referto any of a variety of switches which are self-contained to stand alone.That is, the discrete switch includes some switch mechanism disposedwithin a housing and having a plurality of leads extending from thehousing for electrical connection to the switch. This is distinguishedfrom an elastomer keyswitch of the type described above which isimplemented in some elastomer or arranged on a printed circuit board.FIG. 5 thus includes a switch mechanism housing 56 that encloses aconventional switch.

An existing base plate (or printed circuit board) 64 includes mountingholes 65 and a plurality of clearance holes 68, sized to clear leads (inFIG. 6) that extend from the underside of the switch housing 56.

Force-sensing array 22, keycap 10 and plunger 12 are similar to thosedescribed above. The switch mechanism housing 56 which, in general, is acube-shape, is modified to include an actuator flange 58 extending abouta periphery of the housing as shown. The combined unit is referred tohereafter as a switch/actuator 72. Switch/actuator 72 includes a centralaperture 57 sized to fittingly engage the plunger 12 while allowing avertical sliding motion therein.

The switch/actuator 72 also includes a switch/actuator indexing surface70 extending along a periphery of aperture 57 for contacting the keycapindexing surface 11 as described above. A compliant force distributionpad 60 is sized and shaped to fit between the sensor array 22 andswitch/actuator 72, and, more particularly, to cover the force sensingelements 24. Pad 60 is made from a material similar to rubber dome sheet20. The force distribution pad 60 includes a central aperture 61 sizedand arranged to clear a bottom portion of the switch/actuator 72, asbest seen in FIG. 6. The force distribution pad is formed of aresilient, compliant material such as a foam or rubber material, fordistributing forces applied by the switch/actuator 72 over a surfacearea of the force-sensing elements 24, similar to the rubber dome sheet20 in the embodiments described above.

A pre-load pad 54 is arranged to rest on an upper surface of theactuator flange 58 and includes a central aperture 55 sized to clear theswitch mechanism housing 56. Finally, a pressure plate 52 is sized to atleast cover the pre-load pad 54 and similarly includes a centralaperture 53 sized to clear the switch mechanism housing 56. A pluralityof fasteners 66, for example screws, are disposed to extend through orfrom the base plate 64, through elements 22, 60, 58 and 54, and aresecured into holes 51 provided in the pressure plate 52 for thatpurpose. The arrangement of the mounting holes is not critical, althoughpreferably they are symmetrically arranged about the neutral axis topre-load the force-sensing elements evenly. Where the force-sensorelements 24 are arranged in a square configuration, as shown in FIG. 5,it is convenient to provide the mounting holes in a square configurationrotationally offset by 45° from the square defined by the force-sensorelements, as illustrated.

Referring to FIG. 6, the assembly of FIG. 5 is shown in cross-section inthe standby state. Switch/actuator 72 includes four actuator surfaces59, each of which protrudes from the underside of the actuator flangeregion 58 and is registered with a respective one of the force-sensingelements 24. Spring 75 is a schematic depiction of a conventionalbiasing element which biases plunger 12 upwardly. The compliant forcepad 60 extends between the actuator surfaces 59 and the force-sensingelements 24 to distribute forces transmitted by the actuator surfaces.The pre-load pad 54 and pressure plate 52, as noted, include centralapertures sized to clear the switch mechanism housing 56, therebyproviding a clearance gap 73 therebetween, to allow lateral deflectionof the keycap and plunger, when plunger 12 is fully depressed relativeto actuator 72, without contacting the pressure plate or pre-load pad.The base plate 64 is fastened to the pressure plate 52 to compress thepre-load pad 54, thereby applying a pre-load force to the force-sensingelements as discussed earlier.

Importantly, the switch/actuator 72 is arranged so that a bottom surface74 of the switch housing 56 is spaced from the base plate 64, therebyforming a gap 78 therebetween.

The switch leads 80 extend through clearance holes 68 in the base plateand are electrically connected, for example, to the underside of baseplate 64 (in the case in which the base plate is a printed circuitboard) by flexible leads 82 so that there is essentially no mechanicalcoupling between the switch leads 80 and the base plate. Accordingly,the switch/actuator 72 rests on, and is mechanically supported only by,the actuator surfaces 59. Thus, when the keycap 10 is depressed towardthe base plate so that the keycap indexing surface 11 contacts theactuator indexing surface 70, all forces applied to the keycap 10 by anoperator, including downward or Z axis forces, are transmitted throughelements 72, 59, and 60 to the force-sensor array 22. The clearance gap78 is sized to allow adequate lateral deflections of the keycap andplunger while maintaining the bottom surface 74 spaced from the baseplate 64. The configuration shown and described has no impact on theoverall height of the keyswitch assembly, with the exception of thesmall gap 78. This is particularly advantageous in applications wherethe height profile is critical, such as keyboards in lap-top or"notebook" size computers.

FIG. 7 is an exploded perspective view of an alternative embodiment of adiscrete keyswitch and integrated pointing assembly according to thepresent invention.

FIG. 8 is a cross-sectional view of the assembly of FIG. 7, shown in thestandby state. The reader is by now familiar with the elements shown inFIGS. 7 and 8. Accordingly, this embodiment will be described only byway of comparison to the embodiment of FIGS. 5 and 6. In the embodimentof FIGS. 7 and 8, the pre-load pad 54 and pressure plate 52 arepositioned below the base plate 64, i.e., on a side of the base plateopposite the switch/actuator 72. The assembly is otherwise similar tothe earlier embodiment and functions essentially in the same way. Whilethis embodiment extends slightly below the base plate 64, it has theadvantage of providing clearance above the actuator flange 58. Thisallows the keycap 10 to extend down into the region over the actuatorflange 58 as required in some very low-profile switch configurations.

FIGS. 9 and 10 illustrate yet another embodiment of the presentinvention, again directed to applications that include elastomeric domeor membrane keyswitches as discussed above with respect to FIGS. 1-4.Referring to FIGS. 9 and 10, the base plate 30, sensor array 22, rubberdome sheet 20, guide/actuator 46, keycap 10 and plunger 12 are similarto those described above. Here, however, a pre-load spring assembly 84is provided for pre-loading the four sensor elements. The pre-loadspring assembly 84 is formed of a sturdy yet resilient material such asstainless steel 302 or PH 17-7. The pre-load spring assembly includes aframe portion 85 which is arranged to reside above an upper surface ofthe peripheral flange region of the actuator 46. The frame region 85thus includes a central aperture 90, sized to clear the tower 47 ofactuator 46. Frame portion 85 also includes four depending regions 87,arranged to extend in use alongside the actuator 46. Each of thedepending members 87 is formed to include a respective retaining clip 88adjacent a terminal end of the corresponding depending member. Thepre-load spring assembly 84 also includes a pair of spring elements 86,each extending generally coplanar to the frame region 85. The terminalportions of each spring element 86 define a pair of ears 89, each earextending downward below the plane defined by the frame region 85. Theears 89 contact the guide/actuator 46 at points 91.

The rubber dome sheet 20 includes four elongate slots 94 extendingtherethrough for receiving a respective one of the depending members 87.Similarly, the base plate 30 includes four elongate slots 95 also forreceiving the depending members 87. The depending members are spacedapart sufficiently to avoid contacting the sensor array 22.

Referring now to FIG. 10, the mechanism is assembled so that thepre-load assembly 84 is disposed about the actuator 46 so that each ofthe ears 89 contacts an upper surface of the peripheral flange region ofthe actuator 46. Each of the depending members 87 extends down alongsidethe actuator 46 and through the corresponding slots 94 in the rubberdome sheet 20 and the slots 95 in base plate 30. The retaining clips 88contact the lower surface of base plate 30 so as to retain the pre-loadspring assembly 84 in position. The spring elements 86 exert downwardpressure through the ears 89 on the actuator 46 to pre-load theforce-sensing elements. The embodiment of FIGS. 9 and 10 is otherwisesimilar to the embodiments discussed above with respect to FIGS. 3 and4. The pre-load spring assembly 84 has the advantage of providing boththe pre-loading means and all necessary fasteners within a singleintegral unit. The spring assembly can be stamped out of a suitablemetal and the necessary slots in the other elements can easily bestamped as well, resulting in simple and inexpensive manufacturing.

FIG. 11 illustrates yet another embodiment of the invention. While FIG.4 illustrates a pre-load pad 44 disposed generally above an existingswitch element, and FIG. 2 illustrates a pre-load pad 34 disposed belowthe existing switch element, FIG. 11 illustrates an embodiment in whichpre-load pads 104 are disposed beside an existing switch element.Guide/Actuator 96 is substantially similar to those in FIGS. 2 and 4with the addition of a preload flange 106 disposed just outside theregion containing the curved actuator surfaces 110. Top surface 97 andpreload plate 102 are separated from keyboard top plate 98 by a gap 112.Fasteners 108 retain the preload plate 102 to the base plate 30 whilecompressing pads 104 and flange 106 therebetween. A clearance gap 114 isprovided so the actuator 96 can be rocked without binding. Gap 100allows the actuator 96 to be displaced laterally without contacting topplate 98.

FIG. 12 is a partially broken-away plan view of a keyboard 116 having aplurality of keycaps, like keycaps 118. In arrangement, the system shownis similar to that in FIG. 1.

The keycap and plunger are removed from the "J" key in FIG. 12 to showimportant aspects of the present invention more clearly. Actuator/guide120 is shown beneath top plate 133 through a cutaway view in the topplate.

Actuator/Guide 120 (hereinafter referred to as actuator 120) is similarto actuator 14 in FIG. 1 except that an alternative embodiment is shownusing three force-sensing elements 122, denoted by dotted lines toindicate their location on the underside of the actuator 120, ratherthan four force-sensing elements, like elements 24 in FIG. 1. FIG. 12shows the sensing elements 122 evenly spaced around a central aperture130 of actuator 120. Furthermore, one of the sensing elements ispreferably lined up with a major axis (in this case the Y axis),reducing the complexity of the computations required to derive XYsignals from the sensor information.

A rubber dome 126 is shown indicated by a dotted line below an actuatorindexing surface 132. The tower portion of actuator 120 is separatedfrom the clearance hole 128 in top plate 133 by a working gap, as in theprevious figures. Fastener attachment holes 124 are located midwaybetween the sensing areas and allow fasteners to attach the actuator 120to the preload means beneath the base plate (not shown) as in FIG. 1.

FIG. 13 is a graph of the response of the example FSR force sensingmeans. FSRs change resistance dependent upon the force.

Graph 134 shows this resistance versus force relationship. For forcesbelow 50 grams or so the FSR array is essentially an open circuit. Asthe force is increased from 10 to 100 grams or so, the resistance dropssuddenly as indicated by region 136. Region 136 is characterized byhighly variable operation and is not useful for accurate or repeatableforce sensing.

As the applied force is increased further, to 200 grams or so, theresistance changes stabilize as indicated by region 138. Region 140,denoted by the heavy line, represents the useful operating range of theFSR array, from approximately 200 to 450 grams. One purpose of thepreload means of the present invention is to provide a constant force ofapproximately 300 grams on each of the FSR sensing elements. This bothmoves the FSR operating point into a more linear, repeatable region andallows forces on the actuator to both increase (as an actuator bearsdown) or decrease (as an actuator lifts) forces on the FSR within it'suseful range.

This latter effect of the preload means is very important as iteliminates the need for a central pivot to distribute forces since theforce sensors can now indicate reduced as well as increased loading. Asforces are increased above 700 grams or so, the change in FSR resistanceper additional gram lowers thus resulting in decreased sensitivity.

Having illustrated and described the principles of our invention in apreferred embodiment thereof, it should be readily apparent to thoseskilled in the art that the invention can be modified in arrangement anddetail without departing from such principles. We claim allmodifications coming within the spirit and scope of the accompanyingclaims.

We claim:
 1. A pointing device comprising:a generally flat, rigidreference plate; generally planar force sensing means, disposed inparallel contact on top of the reference plate and having a plurality offorce sensing elements positioned in a predetermined pattern, forsensing force applied to the sensing elements; actuator means disposedon top of the force sensing means and having a plurality of actuatorsurfaces protruding toward the force sensing means, each of the actuatorsurfaces contacting a respective one of the force sensing elements forsupporting the actuator means and for transmitting to the correspondingforce sensing element a force applied to the actuator means; theactuator means being supported solely by the force sensing elements sothat substantially all forces applied by a user to the actuator meansare transmitted to the force sensing means; a generally flat, rigid,backup plate, disposed in parallel to and below the reference plate;resiliently elastic pre-loading means extending between the backup plateand the reference plate; rigid interconnecting means fixed to the backupplate and fixed to the actuator means, without contacting the referenceplate, the interconnecting means sized and arranged so as to compressthe pre-loading means, thereby holding the pointing device sandwichedtogether and pre-loading the force sensing elements so that each forcesensing element provides a respective predetermined output signal in theabsence of an external force applied to the actuator means and so thatthe actuator and the backup plate are movable together in response toexternally applied forces without contacting the reference plate.
 2. Apointing device according to claim 1 wherein:the force sensing means isformed of FSR material and includes at least three force sensingelements symmetrically arranged about a center of the actuator means;each force sensing element exhibits a force to resistance responsecharacterized by a first operating region in which resistance decreaseswith respect to applied force at a first rate, a second operating regionin which resistance decreases approximately linearly with respect toapplied force at a second rate, and a third operating region in whichresistance decreases with respect to applied force at a third rate, thethird rate being substantially less than the first rate and the secondrate being intermediate the first and third rates; and the pre-loadingmeans is arranged to apply a pre-loading force to each force sensingelement adequate to bias said element into the second operating regionin the absence of an externally applied force, so that the symmetricalarrangement of the force sensing elements provides, in response to anexternal force applied tot he actuator off the Z axis, an decreasingresistance in at least one of the force sensing elements and anincreasing resistance in at least one other of the force sensingelements, thereby increasing sensitivity of the apparatus.
 3. A pointingdevice according to claim 2 wherein:the first operating regioncorresponds to an applied force of less than approximately 100 grams;and the second operating region corresponds to an applied force in arange of approximately 200 to 450 grams.
 4. A pointing devicecomprising:a reference plate having a switch; generally planar forcesensing means, disposed in parallel contact with the reference plate andhaving a plurality of force sensing elements positioned in apredetermined pattern, for sensing force applied to the sensingelements; actuator means disposed adjacent the force sensing means andhaving a plurality of actuator surfaces protruding toward the forcesensing means, each of the actuator surfaces contacting a respective oneof the force sensing elements for supporting the actuator means and fortransmitting to the corresponding force sensing element a force appliedto the actuator means; means interconnecting the reference plate and theactuator means for maintaining the actuator surfaces in contact with thecorresponding force sensing elements; the actuator means being supportedsolely by the force sensing elements so that substantially all forcesapplied by a user to the actuator means are transmitted to the forcesensing means; a keycap coupled to the actuator means; the keycapincluding a depending plunger having a predetermined cross-sectionalconfiguration and having a bottom end for actuating the switch and akeycap indexing surface extending along an underside of the keycap; theforce sensing means further including a first central aperture sized toclear the plunger and registered over the switch; the force sensingelements being positioned symmetrically about the first centralaperture; the actuator means further including an upstanding towerportion having a top edge and having a central aperture extendingvertically therethrough and registered over the switch, the towerportion central aperture having a cross-sectional configurationcorresponding tot he cross-sectional configuration of the plunger andsized to fittingly receive the plunger for transmitting lateral force tothe actuator means, while allowing sliding motion therebetween foractuating the switch; the actuator means further including an actuatorindexing surface extending along the top edge of the tower portion andcomplementary to the keycap indexing surface for contacting the keycapindexing surface when the keycap is depressed toward the referenceplate, to transmit to the force sensing elements a Z component of aforce applied to the keycap while the indexing surfaces contact oneanother; the tower portion further having a predetermined heightselected such that the tower portion limits vertical displacement of thekeycap and plunger to a position sufficient to actuate the switch, sothat substantially all forces applied to the keycap in excess of thatnecessary to actuate the switch are transmitted through the actuatormeans to the force sensors; and means for pre-loading the force sensingelements so that each force sensing element provides a respectivepredetermined output signal in the absence of an external force appliedto the actuator means.
 5. A multipurpose keyboard for both typing andcursor control comprising:a reference plate having a plurality of switchcontacts for typing; a keycap having a depending plunger arranged foractuating a selected one of the typing switch contacts; a plurality offorce-sensitive resistors symmetrically disposed about the selectedtyping switch contact and sized and arranged to fit around and clear thesaid switch contact within an area approximately defined by the keycapso that the force-sensitive resistors do not interfere with operation ofthe selected switch contact or any of the switch contacts adjacent theselected switch contact; an actuator positioned over the selected switchcontact and including a central aperture aligned over the selectedswitch contact for receiving the plunger the actuator sized and shapedso as to extend over all of the force-sensitive resistors withoutexceeding the area approximately defined by the keycap so that theactuator does not contact any of the typing switch contacts; theactuator further including a plurality of actuator surfaces, each one ofthe actuator surfaces disposed in constant contact with a correspondingone of the force-sensitive resistors for supporting the actuator in saidposition and for transmitting to the force-sensitive resistors a forceapplied to the actuator, thereby allowing normal operation of thekeyboard for typing as well as sensing forces applied to the said keycapfor cursor control.
 6. A keyboard according to claim 5 furthercomprising:fastening means interconnecting the actuator and thereference plate for maintaining the actuator constant contact with allof the force-sensitive resistors while allowing deflection of theactuator in response to lateral forces without the actuator contactingthe reference plate, so that substantially all external forces appliedto the actuator are transmitted through the actuator surfaces to theforce-sensitive resistors; the fastening means including means forapplying a force to the actuator in the direction of the force-sensitiveresistors, thereby pre-loading the force-sensitive resistors.
 7. Akeyboard according to claim 5 further comprising:a flexible dome sheetoverlying the reference plate and having a plurality of dome springs,each dome spring aligned over a respective one of the switch contacts;and wherein: the keycap plunger is arranged for depressing a selectedone of the dome springs, thereby actuating the corresponding switchcontact; the force-sensitive resistors are symmetrically disposed aboutthe selected dome spring in parallel contact with the dome sheet, andare sized and arranged to fit around the said dome spring within an areaapproximately defined by the keycap so that the force-sensitiveresistors do not interfere with operation of the selected dome spring orany of the dome springs adjacent the selected dome spring; and theactuator is positioned on top of the dome sheet and includes a centralhollowed-out region on the underside, sized and arranged so as to clearthe selected dome spring so that the actuator does not contact theselected dome spring in use.
 8. In a computer keyboard having abaseplate and an array of keycaps, each keycap having a dependingplunger for actuating a corresponding typing switch on the baseplate, amethod of acquiring directional force data through a selected one of thekeycaps for controlling cursor movement, the method comprising:providinga plurality of force sensing elements disposed on the baseplate beneaththe selected keycap; symmetrically arranging the force sensing elementsaround the selected keycap plunger, so that the force sensing elementsdo not interfere with actuation of the corresponding typing switch;providing an actuator positioned on top of the force sensing elementsand supported solely by the force sensing elements, the actuator havinga central aperture sized for receiving the plunger; disposing theselected keycap on top of the actuator with the plunger extending intothe aperture toward the corresponding typing switch; decoupling theselected keycap from the keyboard so as to support the selected keycapsolely by the actuator; limiting downward travel f the selected keycapto a predetermined position adequate for actuating the correspondingtyping switch, so that, upon actuation of the typing switch, alladditional forces externally applied to the selected keycap are coupledthrough the actuator to the force sensing means for cursor control;applying a pre-loading force along a Z axis normal to the base plate soas to force the actuator against all of the force sensing elements inthe absence of an external force on the keycap; selecting thepre-loading force so as to bias the force sensing elements to anintermediate operating point, so that an external force applied to theselected keycap off with the Z axis increases the force on at least oneof the force sensing elements and decreases the force on an opposingelement, thereby providing force information in at least two of theforce sensing elements in response to said deflection of the keycap. 9.A pointing device comprising:a reference plate having a switch; aplurality of force sensing elements disposed in parallel contact withthe reference plate and positioned in a symmetric pattern around theswitch for sensing force applied to the sensing elements; an actuatorhaving a plurality of actuator surfaces, each of the actuator surfacescontacting a respective one of the force sensing elements for supportingthe actuator so that substantially all forces applied by a user to theactuator are transmitted to the force sensing elements; means formaintaining all of the actuator surfaces pressed against thecorresponding force sensing elements thereby holding the pointing devicetogether and preloading all of the force sensing elements; a keycaphaving a depending plunger for actuating the switch and further having akeycap indexing surface extending along an underside of the keycap; theactuator further including a central aperture extending verticallytherethrough and registered over the switch, the aperture sized tofittingly receive the plunger for transmitting lateral force to theactuator means, while allowing sliding motion therebetween for actuatingthe switch; the actuator further including an actuator indexing surfaceextending along the top of the actuator and complementary to the keycapindexing surface for contacting the keycap indexing surface when thekeycap is depressed toward the reference plate, to transmit to the forcesensing elements a Z component of a force applied to the keycap whilethe indexing surfaces contact one another; the actuator height beingselected so as to limit vertical displacement of the keycap and plungerto a position sufficient to actuate the switch, so that substantiallyall forces applied to the keycap in excess of that necessary to actuatethe switch are transmitted through the actuator means to the forcesensors.